1. Field of the Invention
The invention relates to an open-cut mining cutter, particularly for the mining of hard minerals as well as solidified overburden and muck layers. This kind of cutter has a crawler unit including a superstructure and a substructure, a excavating device followed by and a conveyor for the recovered bulk material.
2. Description of the Related Art
Essentially three types of open-cut mining cutters are known and in practical use. These are described, for example, in two technical journals: "Bergbau" [Mining], 8/84, pages 371-376, and "Fordern und Lademaschinen" [Conveying and Lifting] 33 (1983) No. 3, pages 161-165.
One type of cutter are so-called partial cut machines which operate with one or a plurality of rotating cutting heads of relatively small dimensions attached to cantilever arms which can be pivoted up and down as well as sideways. These machines are generally stationary during operation, particularly when used on higher work faces. The recovered material drops onto a loading ramp on the ground and is pulled onto a centrally disposed scraper chain conveyor by means of loading devices such as, for example, lobster claw loaders. The drawback of such devices operating with discontinuous feed is, in particular, their relatively low, greatly fluctuating yield which also depends, inter alia, on the skill and excavating strategy of the operator. The grain size of the bulk material is also subject to great fluctuations and oversizes are difficult to avoid and can only be avoided at the expense of lower yield. Another drawback is the narrow working width compared to the working height -- particularly as a result of the loading device involved -- and the sensitive and wear subjected conveying member, the scraper chain.
A second type of cutter are so-called continuous miners which have a shearing drum arranged transversely between the front and rear crawlers. The drum equipped with helically arranged digging members operates in a rearward-downward direction of rotation. The loosened material is thus pushed to the middle and over a flat loading shield onto the discharge conveyor. The drawbacks of such devices are their limited working width and their low working depth as a result of the absence of the possibility of making a free cut in the region of the drum bearing. Such excavating devices are also not suitable for working hard minerals from thicker layers since the picks are unable to cut themselves free in the working region at the fast rate of advancement and with the circumferential velocity directed in the opposite direction. Further drawbacks are the incomplete transport of the loosened material toward the center and the loading process by way of the loading shield which is connected with great expenditures of force and with wear.
A third type of cutter, so-called surface miners of similar construction as the above-described continuous miners. In contrast to the latter, whose working principle is practically a digging process, these are true cutters. The direction of rotation of the drums equipped with helically arranged picks is forward-upward, i.e. the loosened material must be thrown over and beyond the drum onto the discharge conveyor. In addition to the helical pick arrangement, the drum is provided with gripper strips for this loading process as well as with deflecting walls in front of and above the drum and finally with a shield which pushes the material that has dropped behind the drum over the ground until the drum grips it again. The drawback here is that extensive grain comminution takes place during loosening as well as loading. Similarly to the continuous miners, this type of structure is also able to produce only a relatively small working depth and width. Therefore, high excavating yields necessitate long paths and high processing speeds. This involves not only correspondingly high costs for energy, wear and maintenance but also for the further transport of the recovered material on trucks. Moreover, the marginal conditions of open-cut mining operations are established thereby and in many cases these cannot be combined with economical work planning.
Also known is another open-cut mining cutter which, however, has not yet been constructed ("Schaufelradbagger" [Bucket Wheel Excavator]by W. Durst and W. Vogt, Trans Tech Publications, 1986, page 131.12). The concept of the so-called C-miner is such that the drawbacks of the prior art open-cut mining cutters are avoided and it becomes possible to integrate the device in a continuously operating excavating and transporting system. The excavating device is a three-part trench-cutting drum arranged horizontally at the head. The helically arranged picks of the fast rotating trench-cutting drums are also suitable, just like those of the above-described surface miners, for loosening hard minerals and are supported in the conveying direction by a wear-resistant, double helix on the drum to convey the loosened material from both sides toward the middle Due to the partial overlap of the cutting ranges of the center drum and the side drums, which are arranged at a forward angle, the bearing and drive regions are cut free. In conjunction with the rearward-downward cutting action, this makes possible working heights which lie above the drum diameter. The simultaneous loosening and loading over the entire width of the drum results in quiet operation and uniform comminution of the recovered bulk material to a size which can be transported on a conveyor belt. The arrangement of the excavating device in front of the crawler unit in conjunction with the transport of the material by the helixes and a guide plate or shield arranged vertically behind the drum permits a greater working width than do the above-described open-cut mining cutters. The recovered bulk material is accumulated behind the center drum and is intended to pass through a high passage opening in the center of the shield onto the conveyor belt disposed behind it. This loading principle requires at least very high pushing forces and is encumbered by unsatisfactory efficiency. A further drawback of the C-miner is its limited ability to work thin, hard layers. Due to the rearward-downward direction of rotation, such cases will require the force of a very great weight to prevent the machine from "climbing". As for the other open-cut mining cutters, greater percentages of cohesive material will make recovery even more difficult or impossible since the helixes are clogged by baked-on material and are practically impossible to clean.